NavList:

Frank, you wrote: "I don't think I've ever seen instructions anywhere proposing that the chronometer correction should be interpolated for hours".

Then you haven't read Lärobok i Navigations-Vetenskapen by Carl Anton Pettersson (2nd edition, Stockholm 1861)! In my translation:

"When you know the chronometer's correction at a certain moment and its daily rate, you can easily find the correction for any other moment of time. You have only to multiply the daily rate with the elapsed time, expressed in days and fraction of days, and then, according to ordinary arithmetical rules, add the product to the given correction."

In the three examples that follow this text the author calculates the elapsed time in days with two decimals.

I have seen evidence, from 1897, where the elapsed time was expressed in days with one decimal, and, if I remember rightly, in some case with two decimals. As one unit of the second decimal of a day corresponds to about a quarter of an hour, it seems a little too "precise", but one decimal is probably worth the effort. It could reduce the error after a long spell at sea with many seconds. But of course you cannot know if the result is more correct, until you get an opportunity to check your chronometer.

Lars

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